//用队列实现栈
class MyStack {
    private Queue<Integer> qu1;
    private Queue<Integer> qu2;

    public MyStack() {
        qu1 = new LinkedList<>();
        qu2 = new LinkedList<>();


    }
    
    public void push(int x) {
        if(!qu1.isEmpty()){
            qu1.offer(x);
        }else if(!qu2.isEmpty()){
            qu2.offer(x);
        }else{
            //两个队列都为空指定存放在qu1中
            qu1.offer(x);
        }
    }
    
    public int pop() {
        if(empty()){
            return -1;
        }
        if(!qu1.isEmpty()){
            int size = qu1.size();
            for(int i = 0;i<size-1;i++){
                int x = qu1.poll();
                qu2.offer(x);
            }
            return qu1.poll();
        }else{
            int size = qu2.size();
            for(int i = 0;i<size-1;i++){
                int x = qu2.poll();
                qu1.offer(x);
            }
            return qu2.poll();
        }

    }
    
    public int top() {
        if(empty()){
            return -1;
        }
        if(!qu1.isEmpty()){
            int size = qu1.size();
            int x = -1;
            for(int i = 0;i<size;i++){
                x = qu1.poll();
                qu2.offer(x);
            }
            return x;
        }else{
            int size = qu2.size();
            int x = -1;
            for(int i = 0;i<size;i++){
                x = qu2.poll();
                qu1.offer(x);
            }
            return x;
        }
    }
    
    public boolean empty() {
        //两个队列同时为空的时候 说明模拟实现的栈是空的
        return qu1.isEmpty() && qu2.isEmpty();
    }
}

/**
 * Your MyStack object will be instantiated and called as such:
 * MyStack obj = new MyStack();
 * obj.push(x);
 * int param_2 = obj.pop();
 * int param_3 = obj.top();
 * boolean param_4 = obj.empty();
 */